In an automatic milking system, several milk meters are normally used to measure the amount of milk produced by the milking animals in a herd. Each milking animal may be milked using one or more of these milk meters depending on the milking occasion. The milk meters used are calibrated on a routine basis to ensure that each of them measures the correct amount. This routine will entail unnecessary calibration of some milk meters and at the same time there is a risk that other milk meters have been measuring an incorrect amount of milk during a period of time.
An obvious solution to reduce the number of incorrectly measuring milk meters is to decrease the time between routine calibrations of all milk meters. Another solution could be to regularly check and verify the function of each milk meter, to determine if a milk meter is in need of a calibration, but this will decrease the through put in the automatic milking system.
In an article with the title “A method for continuous automatic monitoring of accuracy of milk recording equipment”, by G. Wendl, X Zenger and H. Auernhammer, published in EAAP Publication No 65, 1992, pages 338 to 345, a method for identifying a malfunctioning or deviating milk meter is disclosed. The method only describes how to identify a malfunctioning milk meter by using previously recorded actual milk yields and comparing them with calculated expected milk yields. The method may also be adapted to automatic milking systems if the time lapsed since the last milking is entered into the calculation of expected yield.
When a malfunctioning milk meter has been identified, a manual re-calibration of the malfunctioning milk meter is performed. The described method is limited in use since it assumes that the systematic error in measurement does not worsen at the same time on all milk meters, that an error in measurement will drift in one direction (directed error), and that the other milking equipment has no defects.